The present invention relates to security documents and, more particularly, to security documents including enhanced means for authenticating the security document.
Conventional security documents, e.g., the void pantograph security documents and the varying tone security documents of U.S. Pat. Nos. 4,579,370, 5,149,140, 5,197,765, 5,340,159, incorporate a security image designed to provide an indication of document authenticity on an attempted duplicate of the document. Often, the nature of the document authentication scheme is described in fine print along the top or bottom of the document--"CASH ONLY WHEN THE COLORED AREA OF THIS DOCUMENT CHANGES GRADUALLY AND EVENLY FROM DARKER TO LIGHTER WITH THE DARKER AREA AT THE TOP" or "THE FACE OF THIS CHECK HAS A SECURITY VOID BACKGROUND PATTERN--DO NOT CASH IF VOID IS VISIBLE." Unfortunately, these printed messages are readily apparent and can be very useful to a potential counterfeiter. Further, these printed message do little to enhance the security of the document on which they are printed and are typically not well-suited for high speed machine authentication.
Accordingly, there is a need for a security document that eliminates the need for readily apparent printed descriptions of the authentication schemes embodied in a document. Further, there is continuing need for security documents incorporating enhanced security features that are well-suited for high speed machine authentication.